1. Field of the Invention
The present invention relates to the methods and devices employed for measuring the driving torque or an associated quantity, especially on a cycle or like vehicle.
2. Description of the Prior Art
In all the systems which exist at the present time such as those described in French patents No. 2,606,876 and No. 2,617,970, for example, the value of the torque to be measured is determined by measurement of a force, of a displacement or of a deformation. The sensitivity of these systems is wholly reproducible but the zero point which corresponds to the measurement information in respect of a zero torque on the driving wheel is subject to variations. These variations may be due for example to a variation in temperature, to creep deformation of material, to permanent deformation, to mechanical friction or to any other disturbing physical phenomenon.
In some measuring instruments in which a similar problem exists, provision is made for a system which enables the user to carry out a zero reset prior to each fresh measurement. This is the case in particular in weighing balances. In these instruments, a certain number of parameters are in fact liable to vary in time and a large number of events (overload or creep, for example) are liable to disturb the measurements. In order to obviate this problem, it is only necessary to provide a system for resetting to zero prior to any fresh measurement since the disturbing phenomena will not subsequently have time to vary during a measurement.
A similar solution could be contemplated only in certain torque-measuring devices which equip cycles in order to permit zero-resetting when the cycle is stationary, namely in devices which make use of measuring gages. On the other hand, a solution of this type would not be suitable in the case of devices which perform a dynamic measurement, for example devices of the type described in French patent No. 2,606,876 since these latter are incapable of providing information on the torque when the driving wheel is not rotating.
Moreover, taking account of the fact that bicycle training sessions are often of very long duration and take place under variable climatic conditions, there is a possibility that the zero point of the measuring device may shift during one and the same utilization of a cycle. In order to solve the problem presented, it is therefore not sufficient to provide a possibility of zero-resetting at a standstill prior to use of a cycle.
It is for the foregoing reasons that the present invention is directed to a method which is specially conceived to ensure that the torque-measuring device fitted on a cycle can be reset to zero during actual use of the cycle provided that this latter has a driving wheel fitted with a free-wheel mechanism.